In time programmed clock thermostats wherein the controlled temperature in a space is changed for comfort or energy saving during certain periods of the day or night, there is a need for manually overriding the time program at the home owner or occupant's will. Such has been done for many years in the T8082A Thermostat shown in the brochure Form No. 60-2416-4 revised 5/81 of Honeywell Inc. When a night time temperature is selected by the time programmed clock, such as 60.degree., the home owner may want to restore the temperature to the day time program. Such is done by a manual changeover button which operates the thermostat switch for the day time temperature. With the need to reduce the cost of such time programmed thermostats, a lower powered motor is used and the associated switch operator must require less power.
The present invention is concerned with a ratchet means for a switch of a time programmed clock thermostat which requires little power and is not greatly biased to prevent movement in a wrong direction. A manual operator for the ratchet means thus must operate in one direction and not produce any drag on the ratchet means in a retracting direction. Specifically, an indexing means is driven by a pawl which is biased against the ratchet means when the pawl is moved in a forward direction and biased away from the ratchet means when returning to an initial position by the use of a cam and cam rider attached to the pawl. With such an invention a large amount of power can be provided to the ratchet means by the pawl and yet the pawl will not adversely move the ratchet means upon its return to the initial position.